To increase our understanding of how relative grain yields in different parts of a paddock in the Mallee region vary year to year (and between crop types) and how these changes are related to soil type and seasonal rainfall.

• Grain yields can vary considerably within the paddock in the Victorian Mallee. The spatial pattern of this yield variation, however, is not always consistent, with relative yield patterns differing over consecutive seasons, and/or crop types, in a flip-flop (alternating) pattern.
• Consistently high yielding zones existed where the shallow subsoil (10-20cm) was a clay loam texture (33% clay) with low salinity. In contrast, consistently low yielding zones possessed a shallow subsoil of light clay (40% clay) and medium to high levels of salinity.
• Flip-flop yield zones were associated with gilgai (crab-hole) depressions where yields tended to increase in dry seasons (due to a concentration of surface water) but decreased in wet seasons (due to water logging of the heavy textured soils). In contrast where gilgai depressions and light textured soils occurred, crop yields were depressed in dry seasons.
• Overall, the flip flop patterns in grain yields observed within paddocks was attributed to the effect of gilgai microrelief and changes in soil texture which influence soil water availability to crops.